High-temperature stable and hydrophobic boron-nitride-modified silica aerogels for heat insulation materials

Abstract

Silica (SiO2) aerogels are widely used in high-temperature insulation materials due to their low thermal conductivity. The hydrophobicity of SiO2 aerogels is considerably important for maintaining high-thermal insulation performance for a long duration. Traditional methods for the hydrophobic modification of SiO2 aerogels involve the modification of organic functional groups present on aerogel surfaces to replace original hydrophilic hydroxyl functional groups. However, due to the thermal damage of functional groups, SiO2 aerogels lose their hydrophobicity at high temperatures (400 °C), which limits the aerogel application in high-temperature fields. This study proposed a new hydrophobic method, chemical vapour deposition, to deposit a layer of hydrophobic boron nitride (BN) on the SiO2 aerogel surface. The surface hydrophobic angle of the BN-modified SiO2 aerogel reached 144.3°, and hydrophobic destruction temperature increased to 700 °C, indicating stable hydrophobicity. The method can be used to a decrease in aerogel surface energy through the deposition of a nano-BN film on the aerogel surface layer while maintaining the porous structure of the unmodified aerogel. The deposited BN layer protects the silica skeleton. This layer inhibits silica crystallisation and improves the thermal stability of aerogels.